The present disclosure relates to a hinge mechanism for an automatic document feeder openably/closably supported on an image reading unit used in digital copiers, image scanners, and the like.
Some conventional image readers mounted in multifunction peripherals and the like employing the electro-photographic process are provided with an automatic document feeder configured to convey sheets of documents one by one to a document placing table (an image reading unit) for reading, and discharges read sheets of documents from the document placing table. Reading methods employable in such an image reader are the following two reading methods. One is a sheet-through method in which, with a document presser closed, a document sheet is read while being automatically conveyed by an automatic document feeder. The other is a document stationary method in which, upon completion of each reading, the document presser is opened and closed in order for a document sheet on the document placing table (a contact glass) to be replaced one by one. In the former, namely, the sheet-through method, a document reading operation is performed with an optical system (scanning means) in the image reader held at a predetermined image reading position without moving for scanning. On the other hand, in the latter, namely, the document stationary method, a reading operation is performed while the optical system is moving for scanning.
With an image reader provided with such an automatic document feeder as described above, because of the weight of the automatic document feeder, a lot of work is required to open/close the document presser for a document reading operation to be performed in the document stationary method. For reduction of such work, there have been proposed various methods where urging force of an elastic member is used to assist the operation of opening/closing the document presser. For example, there has been known a hinge mechanism configured such that, in a state where a document cover (a document presser) is closed, a load torque that biases the document cover in an opening direction remains in a hinge unit.